fix(ci): remove go cache mtime hacks

Cache checks are base on content, not mtimes, no need to hack around it

.travis.yml

@@ -11,9 +11,6 @@ defaults_go: &DEFAULTS_GO
     # so it forces new cache archive on every build
     # remove it before creating cache archive
     - rm -vf $HOME/.cache/go-build/log.txt
-    # force fixed mtime on all files so travis doesn't consider
-    # these as updated
-    - find $HOME/.cache/go-build/ -type f -exec touch -t 201909010000 {} \;
   env:
     - GO111MODULE=on